Embed Size (px)
Citation preview
The Rice brassinosteroid-deficient dwarf2Mutant, Defective inthe Rice Homolog of Arabidopsis DIMINUTO/DWARF1, IsRescued by the Endogenously Accumulated AlternativeBioactive Brassinosteroid, Dolichosterone
Zhi Hong,a Miyako Ueguchi-Tanaka,a Shozo Fujioka,b Suguru Takatsuto,c Shigeo Yoshida,b
Yasuko Hasegawa,a Motoyuki Ashikari,a Hidemi Kitano,a and Makoto Matsuokaa,1
a BioScience and Biotechnology Center, Nagoya University, Chikusa, Nagoya 464-8601, Japanb RIKEN, Institute of Physical and Chemical Research, Wako-shi, Saitama 351-0198, Japanc Department of Chemistry, Joetsu University of Education, Joetsu-shi, Niigata 943-8512, Japan
We have identified a rice (Oryza sativa) brassinosteroid (BR)-deficient mutant, BR-deficient dwarf2 (brd2). The brd2 locus
contains a single base deletion in the coding region of Dim/dwf1, a homolog of Arabidopsis thaliana DIMINUTO/DWARF1
(DIM/DWF1). Introduction of the wild-type Dim/dwf1 gene into brd2 restored the normal phenotype. Overproduction and
repression of Dim/dwf1 resulted in contrasting phenotypes, with repressors mimicking the brd2 phenotype and over-
producers having large stature with increased numbers of flowers and seeds. Although brd2 contains low levels of common
6-oxo-type BRs, the severity of the brd2 phenotype is much milder than brd1 mutants and most similar to d2 and d11, which
show a semidwarf phenotype at the young seedling stage. Quantitative analysis suggested that in brd2, the 24-methylene
BR biosynthesis pathway is activated and the uncommon BR, dolichosterone (DS), is produced. DS enhances the rice
lamina joint bending angle, rescues the brd1 dwarf phenotype, and inhibits root elongation, indicating that DS is a bioactive
BR in rice. Based on these observations, we discuss an alternative BR biosynthetic pathway that produces DS when Dim/
dwf1 is defective.
INTRODUCTION
Brassinosteroids (BRs), a class of steroidal plant hormones, are
structurally defined as C27, C28, and C29 steroids with substitu-
tions on the A- and B-rings and side chains (Fujioka and Sakurai,
1997; Yokota, 1997) and are widely distributed in both lower and
higher plants. Since brassinolide (BL), the most biologically
active BR, was initially isolated and its structure determined in
1979 (Grove et al., 1979), a variety of BRs have been identified in
a broad range of species. To date, >50 BRs have been isolated
and identified from the plant kingdom (Bajguz and Tretyn,
2003). A detailed study of the biosynthesis of BL, a C28 BR, in
Catharanthus roseus and Arabidopsis thaliana revealed that two
parallel routes, the early and late C-6 oxidation pathways, are
connected at multiple steps and are linked to the early C-22
oxidation pathway (Fujioka and Yokota, 2003). In parallel with
biochemical studies on BR, molecular genetic approaches using
BR-deficient and BR-insensitive mutants of Arabidopsis, pea
(Pisum sativum), and tomato (Lycopersicon esculentum) have
greatly contributed to our knowledge of the molecular mecha-
nisms of BRbiosynthesis and signaling (Clouse andSasse, 1998;
Bishop, 2001; Bishop and Koncz, 2002; Fujioka and Yokota,
2003).
In contrast with the rapid advances in research on BRs in
dicots, little is known on the molecular function of BRs in mono-
cots. So far, three types of BR-deficient mutants, d11, d2, and
brd1, and one BR-insensitive mutant, d61, have been isolated.
Molecular biological studies have demonstrated that the genes
containing the d11, d2, and brd1mutations encode cytochrome
P450 enzymes and are involved in the late steps of BR bio-
synthesis (Hong et al., 2002, 2003; Tanabe et al., 2005), and the
D61 gene encodes a putative protein kinase that is very similar to
the Arabidopsis BR receptor BRASSINOSTEROID INSENSI-
TIVE1 (BRI1) (Yamamuro et al., 2000). These studies have
revealed that the monocot rice (Oryza sativa) plant contains
mechanisms for BR biosynthesis and perception that are similar
to those in dicots.
However, no rice mutation has yet been identified in the
biosynthetic pathways of sterols, which are precursors of BRs;
consequently, it is not yet known whether the sterol biosynthetic
pathway in rice or other monocots is similar to that in dicots.
Recently, a maize (Zea mays) gene, dwf1, was cloned, and its
high sequence similarity to the Arabidopsis homologDIMINUTO/
DWARF1 (DIM/DWF1) suggested thatmonocots and dicots have
similar sterol biosynthetic pathways (Tao et al., 2004). However,
the absence of a monocot sterol biosynthesis mutant has thus
far hampered the understanding of BR and other sterol-based
1 To whom correspondence should be addressed. E-mail [email protected]; fax 81-52-789-5226.The author responsible for distribution of materials integral to thefindings presented in this article in accordance with the policy describedin the Instructions for Authors (www.plantcell.org) is: Makoto Matsuoka([email protected]).Article, publication date, and citation information can be found atwww.plantcell.org/cgi/doi/10.1105/tpc.105.030973.
The Plant Cell, Vol. 17, 2243–2254, August 2005, www.plantcell.orgª 2005 American Society of Plant Biologists
phytohormones in agriculturally important monocot plants. The
sterol mutants of dicots fall into two groups. Members of the first
group contain a lesion in the late steps of the sterol biosynthetic
pathway. The phenotypes of these mutants, such as ste1/bul1/
dwf7 (Choe et al., 1999b; Catterou et al., 2001), le/cro6/dwf5
(Serrano-Cartagena et al., 1999;Choe et al., 2000), anddim/dwf1
(Takahashi et al., 1995; Klahre et al., 1998), cannot be distin-
guished from BR-deficient mutants and can be rescued by
treatment with exogenous BL. By contrast, members of the
second group are defective in the early steps of sterol bio-
synthesis. These mutants, such as cph/smt1 (Diener et al., 2000;
Schrick et al., 2002), cvp1/smt2 (Carland et al., 1999, 2002), and
ell/hyd2/fackel (Jang et al., 2000; Schrick et al., 2000; Souter
et al., 2002), share some of the characteristics of BR-deficient
mutants but also have unique defects during embryogenesis that
cannot be rescued by BR treatment. If rice sterol biosynthesis is
similar to that of dicots and rice sterols have biological functions
similar to dicot sterols, it should be possible to isolate mutants
defective in sterol biosynthesis from rice mutant stocks by
screening for BR-related phenotypes.
Here, we report the isolation and characterization of a rice BR-
deficient mutant, BR-deficient dwarf2 (brd2). Molecular genetic
studies have revealed that brd2 is a loss-of-function allele ofDim/
dwf1, a gene homologous to the Arabidopsis DIM/DWF1. Al-
though the level of common endogenous BRs is severely re-
duced in brd2, the abnormalities of the mutant are less severe in
the early vegetative stage. Feeding experiments and quantitative
analysis of sterols and BR intermediates have revealed that the
brd2 mutant accumulates an active BR, dolichosterone (DS),
which is not detected in the wild type. Our data suggest that the
weak phenotype of brd2 is caused by the production of DS in
a Dim/dwf1-free BR biosynthetic pathway.
RESULTS
Characterization of brd2
Since the identification of the first rice BR-related mutant, d61,
which is defective in the rice Bri1 gene (Yamamuro et al., 2000),
we have collected rice dwarf mutants with phenotypes similar to
d61 to investigate the mechanisms of BR biosynthesis and
signaling in rice.We have also previously isolated three other BR-
related mutants, brd1, d2, and d11, all of which are defective in
BR biosynthesis owing to mutations in BR C-6 oxidase (Cyp85),
Cyp90D2, and Cyp724B1, respectively (Hong et al., 2002, 2003;
Tanabe et al. 2005). Recently, we identified a dwarf mutant, brd2,
which displays the typical BR-deficient phenotype but also has
characteristics not observed in the other mutants. Figure 1A
shows the gross morphology of the mutant in an early vegetative
stage. At this stage, the mutant plant (right) displays a moderate
dwarf phenotype with a height;70% of the wild-type plant (left)
but no other obvious abnormalities. However, as development
progresses, the phenotype becomes more severe with charac-
teristics typical of BR-related mutants: dark-green, erect leaves
and shortened leaf sheaths. After flowering, the height of the
plant reaches only;40% of the wild type (Figure 1B). We com-
pared the internode elongation patterns of brd2, the wild type,
and other BR-deficient mutants (Figure 1C). In the wild type, the
five uppermost internodes elongate; the internodes are num-
bered from top to bottom such that the uppermost, just below
the panicle, is designated as the first internode (Figure 1C).
By contrast, the three BR-deficient mutants show different
Figure 1. Phenotype of the brd2 Mutant.
(A) Gross morphology of wild-type (left) and brd2 (right) seedlings grown
for 40 d in soil. Bar ¼ 10 cm.
(B)Gross morphology of field-grown wild type (left) and brd2 (right) at the
flowering stage. Bar ¼ 15 cm.
(C) Comparison of the internode elongation pattern of brd2 with pre-
viously characterized rice BR-deficient mutants. The five uppermost
internodes (I to V) of the wild type were elongated. Bar ¼ 10 cm.
(D) Panicle structure. Thewild-type plant (left) developed;120 seeds per
panicle, and thebrd2mutant panicle developed;30 seedswith poor ger-
mination rates. Arrows indicate the positions of the nodes. Bar ¼ 10 cm.
(E) Morphology of unhulled grains (top) and brown rice (bottom). The
mutant (right) produced shortened grains. Bar ¼ 1 cm.
(F) Root morphology. Seedlings were grown at 308C in water for 1 week
in the light. Bar ¼ 1 cm.
2244 The Plant Cell
elongation patterns: d2-1 has a specific inhibition in the second
internode, brd1-1 is completely defective in internode elonga-
tion, and the first internode of brd2 elongates, but the lower
internodes do not (Figure 1C).d61-2, which is defective in the rice
Bri1 gene, also exhibits dwarfism with a lack of internode
elongation except for the first internode (Yamamuro et al.,
2000). The brd2 mutant flowers and produces malformed pani-
cles, but the numbers of spikelets and rachis branches, aswell as
fertility, are severely reduced (Figure 1D). The lengths of the first
and second rachis branches in the panicle are also severely
reduced. In contrast with these severe defects, the neck in-
ternode of the mutant is longer than that of the wild type (Figure
1D). This phenomenon is a common feature in rice BR-related
mutants because long neck internodes are also observed in d2
and d61-1. In addition, the brd2 mutant also exhibits shortened
grains (Figure 1E) and defective root elongation and develop-
ment (Figure 1F). Although one seminal root develops normally
during embryogenesis, after germination the seminal root elon-
gates to only two-thirds of the wild-type root and formation of
the crown root is inhibited, but lateral root formation is not as
severely affected as crown root formation.
brd2 Is a Knockout Allele of the Dim/dwf1Gene
To isolate Brd2 by positional cloning, we first performed rough
mapping of brd2 using 30 F2 progeny with the dwarf phenotype.
Using 62 molecular markers, the brd2 locus was mapped to rice
chromosome 10 between 21.8 and 30.2 centimorgan. Because
a gene homologous to Arabidopsis DIM1/DWF1 is present in this
area,we suspected thatbrd2was identical toDim/dwf1 (Figure 2A).
The predicted Dim/dwf1 protein consists of 561 amino acids with
80% identity to the Arabidopsis DIM/DWF1 sequence, and com-
parison of the genomic and full-length cDNA sequences showed
that Dim/dwf1 contains three predicted exons (Figure 2B). Direct
Figure 2. Molecular Characterization of the brd2 Mutation.
(A) The brd2 mutation was mapped at ;25 centimorgan on chromosome 10, near the map position of Dim/dwf1.
(B) Schematic diagram of the structure of Dim/dwf1 and the site of the mutation in the brd2 allele. Closed boxes represent exons, and open boxes
indicate introns. The first Met (ATG) and the stop codon (TAA) are located in exons 2 and 3, respectively. The single base deletion in the brd2 allele is
indicated by an arrow, and the premature stop codon is marked with an asterisk.
(C) The deduced amino acid sequence of Dim/dwf1. The mutation site is marked with a closed triangle, and the FAD binding domain is underlined.
(D) Levels ofDim/dwf1 transcripts in wild-type (left) and brd2 (right) plants. Ten micrograms of total RNAwas loaded per lane. Ethidium bromide–stained
rRNA bands were monitored as a loading control.
(E) Molecular complementation. Transgenic plants derived from mutant callus transformed with the Dim/dwf1 gene had the wild-type phenotype, in
contrast with the dwarf phenotype of the mutant (right), and transformants containing the empty vector had the dwarf phenotype (left).
(F) Organ-specific expression of the Dim/dwf1 gene in the wild type. RT, root; SA, shoot apex; LB, leaf blade; LS, leaf sheath; ST, stem; PA, panicle; FL,
flower. Five micrograms of total RNA was loaded per lane, and ethidium bromide–stained rRNA bands were monitored as a loading control.
(G) The effect of BL on Dim/dwf1 expression. Total RNA was isolated from wild-type, brd1-1, and d61-2 seedlings either treated for 10 d with a final
concentration of 1 mM BL (þ) or untreated (�); 7.5 mg was loaded per lane.
An Uncommon BR Biosynthetic Pathway 2245
sequencingof thebrd2mutant allele revealeda singlebasedeletion
(guanine) in exon 2, which leads to a frameshift and produces
a premature stop codon near the mutation site (Figure 2B). The
mutationcauses the lossof themajority of aconservedFADbinding
domain and the C-terminal region in Dim/dwf1 (Figure 2C).
We used gel blot analysis to examine the level of Dim/dwf1
transcripts in the mutant. RNA from 10-d-old light-grown wild-
type and mutant seedlings was isolated and probed with the
;800-bp 39 fragment of the Dim/dwf1 cDNA. The Dim/dwf1
transcript was detected in wild-type seedlings but not in the
mutant (Figure 2D). A wild-type genomic DNA fragment contain-
ing the entire Dim/dwf1 was transformed into brd2, which re-
stored the wild-type phenotype in all plants that were resistant to
the selection marker, hygromycin (Figure 2E, right). Transforma-
tion with the empty vector had no effect on the dwarf phenotype
(Figure 2E, left). Based on these results, we predict that brd2 is
a knockout allele of Dim/dwf1.
The Dim/dwf1 expression pattern in various organs was
studied using RNA gel blot analysis. Dim/dwf1 transcripts were
detected in all organs examined, albeit at different levels. The
highest expression was in stems; intermediate expression was
seen in roots, the shoot apex, and flowers; and expression
was low in leaves and panicles (Figure 2F). RNA gel blot analysis
was also used to examine the effect of exogenously applied BL
on Dim/dwf1 expression (Figure 2G). Similar Dim/dwf1 expres-
sion levels were observed in the wild type, the BR-deficient
mutant brd1, and d61-2, which is partially defective in the BR
signaling pathway (Yamamuro et al., 2000), and expression was
not affected by treatment with BL. These results indicate that
Dim/dwf1 expression is not regulated by BL, in contrast with D2
andBRD1, which are downregulated byBL in a feedbackmanner
(Hong et al., 2002, 2003).
Overexpression and Suppression of Dim/dwf1
in Transgenic Rice Plants
Because only one brd2mutant was isolated in the first screening,
we attempted to isolate other brd2 alleles fromourmutant stocks
and the rice Tos17 insertion mutant library, but no other alleles
were found in these libraries. Therefore, we produced transgenic
plants expressing antisense and sense Dim/dwf1 transcripts
under the control of the rice Actin constitutive promoter (McElroy
et al., 1990). Antisense and sense Dim/dwf1 transgenic plants
showed contrasting phenotypes in plant height (dwarf versus tall)
(Figure 3A), lamina joint bending (erect versus bent) (Figure 3B),
the panicle (decreased versus increased spikelets) (Figure
3C), and internode elongation (stunted versus elongated) (Figure
3D), respectively. The overall phenotype of antisense plants was
similar tobrd2, although the abnormalities of the antisense plants
were less severe than in brd2. The gross morphologies of the
transformant lines confirm that the brd2 phenotype is caused by
a defect in the functioning of Dim/dwf1. We performed RNA gel
blot analysis using two different probes to confirm changes in the
levels of Dim/dwf1 mRNA in the transgenic plants (Figure 3E).
When the entire cDNA sequence was used as a probe, the inten-
sity of the hybridized band in both antisense and sense plants
was greater than in wild-type plants, indicating that the antisense
and sense RNAs are highly expressed in the transgenic lines.
Figure 3. Phenotypes of Dim/dwf1 Antisense and Sense Transgenic Plants.
(A) Gross morphology of an antisense plant (left), a control plant
containing the empty vector (middle), and a sense plant (right) 3 months
after transplantation. Bar ¼ 20 cm.
(B) Leaf morphology: a wild-type leaf (center) bends away from the
vertical axis of the leaf toward the abaxial side, an antisense leaf (left) is
more erect, and that of an overproducer (right) is more bent.
(C) Panicle structure: the antisense plant (left) generates poor panicles
with lower spikelet numbers than the wild type (center), whereas the
overproducer (right) generates superior panicles with increased spikelet
numbers.
(D) Internode elongation pattern. The antisense plant (left) is severely
inhibited in the elongation of internodes II through V, whereas the
overproducer has increased numbers and lengths of elongated intern-
odes in comparison with the wild type (center). Bar ¼ 20 cm.
(E) RNA gel blot analysis of the endogenous and transformed Dim/
dwf1 transcripts. Two micrograms of total RNA was loaded per lane. An
800-bp cDNA fragment containing the coding sequence was used as
a probe to detect both sense and antisense Dim/dwf1 transcripts (top),
and a 200-bp probe containing only the 39-noncoding sequence of the
Dim/dwf1 transcript was used to detect endogenous Dim/dwf1 expres-
sion (middle). Ethidium bromide–stained rRNA bands were monitored as
a loading control (bottom).
2246 The Plant Cell
When the 39-untranslated sequence, which was not included in
the transgene in the antisense or sense constructs, was used as
a probe, either no band or a band of very low intensity was
observed in the antisense plant samples, and a strong band of an
intensity similar to the wild type was observed in the sense plant
samples (Figure 3E). The RNA gel blot analysis confirms that the
phenotypes observed in the antisense and sense plants are
caused by lower and higher expression ofDim/dwf1, respectively.
Common BR Levels Are Much Lower in brd2 Than in
d2 or d11, but the Dwarfism of brd2 Is Most Similar
to That of d2 and d11
We compared the levels of BR intermediates in brd2 and wild-
type seedlings to identify themetabolic step that is blocked in BR
biosynthesis. As shown in Figure 4, intermediates from cam-
pesterol (CR) to castasterone (CS), in either the early or late C-6
oxidation pathways, were dramatically decreased in the brd2
mutant. No BL was detected in the shoots of either mutant or
wild-type plants. The precursor of BL, CS, which is predicted to
be the most bioactive BR in rice because BL has not yet been
detected in this species (Yamamuro et al., 2000; Hong et al.,
2002, 2003), was detected in the wild type, whereas no or a very
low level of CS was detected in brd2 in the two independent
experiments, confirming that the mutant is deficient in the
biosynthesis of the active BR. Because Arabidopsis DIM/DWF1
has been proposed to catalyze the conversion of 24-methylene-
cholesterol (24-MC) to CR (Klahre et al., 1998), we also mea-
sured the levels of 24-MC and CR in wild-type and brd2 plants.
In the mutant, the level of CR was decreased >100-fold, and
the level of 24-MC was increased >10-fold relative to the wild
type, demonstrating that rice Dim/dwf1 catalyzes the conversion
of 24-MC to CR, as does Arabidopsis DIM/DWF1.
Although the Arabidopsis and rice DIM/DWF1 proteins cata-
lyze the same step in the BRbiosynthetic pathway, the severity of
the knockout mutants of these genes differs, with the Arabidop-
sis DIM/DWF1 knockout mutant showing a severely abnormal
phenotype (Takahashi et al., 1995) and the rice Dim/dwf1
Figure 4. Quantitative Analysis of Endogenous BR Intermediates in Wild-Type and brd2 Plants.
Shoots of wild-type and mutant plants were harvested after growth in a greenhouse for 2 months. BR levels (ng/g FW) in wild-type (left) and brd2 (right)
plants are shown below each product. BR levels were measured in two independent experiments. na, not analyzed; nd, not detected.
An Uncommon BR Biosynthetic Pathway 2247
knockout mutant showing a moderate phenotype at an early
vegetative stage (Figure 1A). Genomic DNA gel blot analysis was
performed to examine the possibility that the rice genome
contains an additional Dim/dwf1 homolog. Even under low-
stringency conditions, only bands derived from Dim/dwf1 itself
hybridized with the Dim/dwf1 cDNA probe. In addition, no
homolog of Dim/dwf1 in the rice genome was identified in
a tBLAST search for proteins with similarities to Arabidopsis
DIM/DWF1 and rice Dim/dwf1 (data not shown).
To reconcile the inconsistency between the phenotype and the
level of the active BR, CS, in brd2, we also compared the levels of
BR intermediates and the phenotypic severity of the rice BR-
deficientmutants previously isolated (Figure 5).Mutants showing
a mild phenotype, such as d2-1, d2-2, d11-1, and d11-2,
contained some CS (0.10 to 0.38 ng/g fresh weight [FW]),
6-deoxocastasterone (6-DeoxoCS) (0.54 to 1.27 ng/g FW), and
typhasterol (TY) (0.40 to 0.64 ng/g FW),which corresponded from
aquarter to a similar level as in thewild type. By contrast,mutants
showing severe phenotype, such as brd1-1, brd1-2, and brd1-3,
contained undetectable levels of CS and 0.04 to 0.18 ng/g FW of
TY, whereas the level of 6-DeoxoCSwasmuch higher than in the
wild type because thesemutants are defective in BRC6-oxidase.
When we compared brd2 with these BR-deficient mutants, the
dwarfism of brd2 was most similar to d2-1 and d11-2, whereas
the amounts of three BRs were 0.01 or undetectable (Figure 5).
An Alternative BR Biosynthetic Pathway Produces an
Uncommon Bioactive BR in Rice
The trace levels of CS in the brd2 mutant, which shows a
moderately abnormal phenotype, suggest that an alternative
BR biosynthetic pathway may function in the mutant and may
produce one ormore alternative bioactive BRs that attenuate the
severity of the phenotype. Figure 6 shows the proposed normal
and alternate BR biosynthesis pathways. The bioactive CS is
synthesized via a Dim/dwf1-requiring pathway with the conver-
sion of 24-MC to CR, as mentioned above. Measurements of the
levels of all BR-related compounds in these pathways showed
that Dim/dwf1 was also necessary for the isomerization and
reduction of the D24(28) bond of isofucosterol to produce sitos-
terol. Three alternative pathways are expected to be activated
when D24(28) isomerization and reduction are defective: the 28-
nor–type pathway with 28-norcastasterone as the end product,
the 24-methylene–type pathway with DS as the end product,
and the 24-ethylidene–type pathway with 28-homodolichoster-
one as the end product (Figure 6). The first possibility, the
28-nor–type pathway, is less likely because in brd2, the level of
a key precursor, cholesterol, was less than the level in the wild
type, and the end product of this pathway, 28-norcastasterone,
was undetectable. The 24-ethylidene–type pathway, the last
possibility, was found to be activated in brd2, and the levels of
intermediates in this pathway, such as isofucosterol, 24-ethyl-
idenecholest-4-en-3-one, and 24-ethylidenecholestanol, were
greatly increased, but the expected end product, 28-homodo-
lichosterone, could not be detected. Thus, it is difficult to
conclude that the 24-ethylidene–type pathway contributes to
the production of an alternative bioactive BR in the mutant.
The most likely pathway for the production of an alternative
bioactive BR is the 24-methylene–type pathway. The levels of
intermediates in this pathway were strongly increased in brd2,
and the end product of this pathway, DS, which was previously
reported to be present in rice (Abe et al., 1984), also accumulated
in the mutant but was undetectable in the wild type. Because we
did not have an internal standard for DS, we could not estimate
its intrinsic level. The endogenous amount of DS should be higher
than the raw value, which is presented as the amount of DS in
Figure 6. If the recovery rate of DS is the same as that of
BL (55%), the expected level of DS in brd2 is estimated to be
;0.20 ng/g FW,which is approximately half of the CS (;0.40 ng/g
FW) found in the wild type.
DS Has Biological Activity Similar to CS in Rice
To examine the possibility that the bioactivity of DS compensates
for decreased levels of CS in the brd2 mutant, DS feeding
Figure 5. Comparison of Dwarfism and Level of BRs between brd2 and
Other Rice BR-Deficient Mutants.
(A) Two-week-old seedlings are shown. The mutants were germinated
and grown in MS agar. The background of d2-1, d2-2, and d11-1 is T65
(Taichung 65); brd2, brd1-1, brd1-2, and brd1-3 are Ni (Nipponbare)
background; and that of d11-2 is Shi (Shiokari). Bar ¼ 5 cm.
(B) Comparison of the level of TY, 6-DeoxoCS, and CS in the BR-
deficient mutants. The background plant of each mutant is written in
parentheses. The level of BRs in d2, d11, brd1-1, and brd1-2 are adopted
from the results previously reported (Hong et al., 2002, 2003; Tanabe
et al., 2005). CS level in brd1-3 was not determined because of
contamination with unknown compound(s).
2248 The Plant Cell
Figure 6. The Sterol Biosynthetic Pathway and Sterol Contents in the Wild Type and brd2.
An Uncommon BR Biosynthetic Pathway 2249
experiments were performed using wild-type and BR-related
mutants. We first compared the effects of DS and CS on the
growth of brd1-1, a knockout mutant of BR C-6 oxidase. CS was
found to promote the elongation of leaf sheaths and to rescue the
abnormal morphology of newly expanded leaves after a 2-week
exposure. Mutant plants treated with DS also grew elongated
leaf sheaths, though the effect of DSwas somewhat weaker than
that of CS. Similarly, the morphology of newly expanded leaves
was rescued by treatment with DS (Figure 7A).
Lamina joint bending tests were also performed using wild-
type, brd2, and d61-2 leaves (Figure 7B). This assay exploits the
high sensitivity of the degree of bending between the rice leaf
sheath and blade to exogenously applied bioactive BRs. In the
wild type, both CS and DS increased lamina joint bending in
a dose-dependent manner, with CS being slightly more active
than DS. DS was more effective than CS at increasing the
bending of the lamina joints in the brd2mutant. In d61-2, a loss-
of-function mutant of the BRI1 receptor kinase, neither CS nor
DS increased lamina joint bending, indicating that DS and CS are
similarly perceived by the BRI1 receptor.
The effects of CS and DS on root elongation in wild-type, brd2,
and d61-2 seedlings were also examined (Figures 7C and 7D).
Treatment of wild-type plants with 10�7 M CS or DS severely
inhibited root elongation, although the inhibitory effect of DS was
slightly weaker than that of CS (Figure 7C). Both compounds also
inhibited root elongation in brd2. By contrast, the elongation of
d61-2 roots was not inhibited by CS or DS. The inhibition of wild-
type root elongation by CS and DS was dose dependent from
10�9 to 10�7 M, and the inhibitory activity of CS was always
higher thanDSat$10�9M. Inbrd2, CS andDSalso inhibited root
elongation in a dose-dependentmanner from10�9 to 10�6M, but
the inhibitory effects were similar at the same concentrations.
However, neither CS nor DS inhibited root elongation in the BR-
insensitive mutant at concentrations of 10�7 M or lower, whereas
both compounds slightly inhibited root elongation at 10�6M,with
CS having a slightly stronger effect than DS. These results
support the observation in the lamina joint bending test that DS is
a bioactive BR with slightly less activity than CS in the wild type,
but in brd2, DS is as bioactive as CS.
DISCUSSION
This study demonstrates that a knockout mutation, brd2, of the
rice gene encoding a protein similar to the Arabidopsis DIM/
DWF1 causes a semidwarf phenotype in the vegetative stage,
with severe defects in internode elongation and panicle and seed
development. Quantitative analysis of the endogenous sterol
levels showed that brd2 is defective in the conversion of 24-MC
to CR, as are the Arabidopsis dim/dwf1 and pea lkb mutants
(Nomura et al., 1999; Schultz et al., 2001). The weak phenotype
of brd2 during vegetative growth cannot be explained by the
residual levels of CS but is probably due to DS produced in the
absence of adequate BRs from other pathways. DS has BR
activity in rice plants, such as promoting the angle of bending of
the lamina joint and inhibiting root elongation.
brd2 Exhibits Features Not Observed in Previously
Isolated Rice BR-Related Mutants
Rice BR-related mutants can be distinguished from other rice
dwarf mutants by their distinctive internode elongation features
(Figure 1C). The group of BR-related mutants that includes the
mutants d2, d11, and d61-1 hadweak phenotypes and a specific
reduction in the second internode. Mutants brd2 and d61-2, with
intermediate phenotypes, had a specific reduction from the
second to the fourth internodes. Mutants with severe pheno-
types, brd1-1 and brd1-2, only elongated at the neck internode.
The overall severity of rice BR-related mutants can be repre-
sented by these unique internode elongation patterns. For ex-
ample, the mutants of the d2, d11, and d61-1 group show mild
dwarfism of leaves in the vegetative stage and slightly shortened
yet fertile grains. By contrast, the mutants of the brd1-1 and
brd1-2 group form severely stunted and malformed leaves at
the vegetative stage and very small numbers of flowers, which
are malformed and infertile. However, the overall phenotype of
brd2 does not match either group, although this mutant has a
specific reduction in the second to fourth internodes. For ex-
ample, brd2 has mildly dwarfed leaves but no other abnormal
morphologies. The phenotype is similar to that of thed2,d11, and
d61-1 group, all of which form erect leaves with slightly stunted
sheaths. In contrast with its mild phenotype in the early seedling
stage, brd2 is much more severely affected at the developing
flower stage than the d61-2 group, approaching that of brd1-1
and brd1-2. The fertility of brd2 is low, as it is difficult to obtain
seeds from plants homozygous for brd2, but d61-2 forms fertile
flowers and develops viable seeds. Therefore, the phenotype of
brd2 is intermediate between mild and severe as growth pro-
gresses, a feature that is unique tobrd2. It is possible that the brd2
phenotype is caused by an unusual mechanism related to BR
biosynthesis.
The brd2Mutation Is a Knockout of Rice Dim/dwf1
We concluded that the brd2 mutation is caused by a knockout
of Dim/dwf1 for several reasons. First, Dim/dwf1 in brd2 con-
tains a single base deletion in exon 2, which leads to a premature
stop codon approximately two-thirds of the way through the
coding region, causing the production of a nonfunctional protein
(Figure 2B). Second, theDim/dwf1 transcript is not detected in the
mutantbut is in thewild type (Figure 2D). Third, transformationwith
Figure 6. (continued).
Proposed biosynthetic pathways of the wild type (left) and brd2 (right) are shown. The end products of theDim/dwf1-requiring pathways are enclosed in
boxes with solid lines, and those of the Dim/dwf1-free pathway are enclosed in boxes with dashed lines. Sterol levels were measured by two
independent experiments. The level of DS was not corrected by an internal standard. The number of arrows does not represent the number of chemical
reaction steps. nd, not detected.
2250 The Plant Cell
wild-typeDim/dwf1 rescues themutant phenotype ofbrd2 (Figure
2E). Fourth, the phenotype of plants transformed with the anti-
sense cDNA mimics the abnormal phenotype of brd2 (Figure 3).
Finally, in the mutant, the level of 24-MC is greater than in the wild
type, whereas the level of CR is dramatically decreased (Figure 4),
as in the Arabidopsis dimmutant and the pea lkbmutant.
Klahre et al. (1998) studied the function of Arabidopsis DIM/
DWF1 by analyzing the dim mutant, revealing that dim accumu-
lates 24-MC and shows a deficiency in CR. Using deuterium-
labeled sterols, the authors also showed that DIM/DWF1 is
involved in both the isomerization and reduction of the D24(28)
bond. A similar accumulation of 24-MC and deficiency in CRwas
observed in the Arabidopsis dwf1 mutant, which is allelic to dim
(Choe et al., 1999a), and also in the pea lkbmutant (Nomura et al.,
1999). Taking all of these observations together, although there is
no direct biochemical evidence that the DIM/DWF1 protein
Figure 7. BR Biological Activity of DS.
(A) Phenotypic rescue of the abnormal morphology of brd1-1 by treatment with DS and CS. The malformed phenotype and shortened leaf sheaths of
a brd1-1 plant grown for 4 weeks were not rescued by the mock treatment (cont.), whereas 1 mM DS or CS restored the sheath elongation and
morphology of newly expanded leaves. White brackets indicate the relative length of the uppermost leaf sheaths.
(B) Lamina joint bending test. DS increased the lamina joint bending of the wild type and brd2 in a dose-responsive manner but not of the BR-perception
mutant d61-2. CS treatment had an effect similar to DS treatment, although the efficiency of CS was slightly higher than that of DS in the wild type and
lower in brd2. Shown at right are typical lamina joint bending results after treatment with 1 mg CS or DS.
(C) Inhibition of root elongation by treatment with DS or CS. Plants were germinated on agar lacking (�BR) or containing 10�7 M CS or DS. Seedlings
were examined 4 d after germination.
(D) Effect of CS and DS on root elongation in wild-type, brd2, and d61-2 seedlings. The plants were germinated as in (A) with the indicated
concentrations of CS or DS. The data presented are the means of results from six plants. Error bars ¼ SD.
An Uncommon BR Biosynthetic Pathway 2251
catalyzes the isomerization and reduction of the D24(28) bond, it is
possible that the Arabidopsis and pea DIM/DWF1 proteins
catalyze the conversion of 24-MC to CR in the synthesis of
bioactive BRs in these plants. By analogy, rice Dim/dwf1 should
also be involved in the isomerization and reduction of the D24(28)
bond to convert 24-MC to CR in rice (Figure 4).
DS Functions as a Bioactive BR in Rice
There are three possible hypothetical pathways for sterol me-
tabolism in brd2, in which the isomerization and reduction of the
D24(28) bond are impaired: the 28-nor–type, the 24-methylene–
type, and the 24-ethylidene–type pathways (Figure 6). Nomura
et al. (1999) previously discussed the possibility that plants
defective in DIM/DWF1 may not show a clear dwarf phenotype
because they can synthesize C27-type BRs, probably from
cholesterol, which would compensate for decreases in CR-
derived BRs, such as BL and CS. This postulated pathway,
derived from cholesterol, is the same as the first hypothesized
pathway but is not functional in the brd2 mutant. Actually, the
level of cholesterol is decreased, not increased, in the mutant. In
contrast with the 28-nor–type pathway, the 24-methylene– and
24-ethylidene–type pathways are activated in the mutant, and
the levels of 24-methylene–type and 24-ethylidene–type sterols
are greatly increased (Figure 6). Similarly, the Arabidopsis dim/
dwf1 and pea lkbmutants accumulate relatively large amounts of
24-MC and isofucosterol (Klahre et al., 1998; Nomura et al.,
1999), indicating that sterol metabolism of the 24-methylene and
24-ethylidene types is activated in various plant species that are
defective in isomerization and reduction of the D24(28) bond.
Klahre et al. (1998) proposed the activation of a 24-methylene–
type pathway, which converts 24-MC to 24-methylenecholesta-
nol, in the Arabidopsis dim mutant by analogy with the pathway
from CR to campestanol. Evidence in brd2 suggests that the rice
BR-metabolizing enzymes also catalyze the steps from24-MC to
DS. By analogy, it is possible that the enzymes in other plants
also catalyze the steps from 24-MC to DS to accumulate DS in
dim/dwf1 mutants of other plant species. Further analysis of the
sterol content in dim/dwf1 mutants should help to elucidate this
hypothesis.
The high levels of sterols, such as 24-methylenecholestanol
and 24-ethylidenecholestanol, in the brd2 mutant suggest that
BRs containing 24-methylene and 24-ethylidene groups also
accumulate in themutant. This was found to be true in the case of
the 24-methylene–type BR, and the level of DS was increased
in themutant, whereas 28-homodolichosterone, the end product
of the 24-ethylidene BR pathway, was not detected. The lack of
production of 28-homodolichosterone in the mutant may be
caused by a low or complete lack of affinity of BR-metabolizing
enzymes for 24-ethylidene–type BRs because no 28-homocas-
tasterone was detected in wild-type plants, even though high
levels of its precursor, sitostanol, were detected (Figure 6).
The biological activity of DS in rice was confirmed by feeding
experiments using three different BR-responding phenomena in
rice: the rescue of leaf sheath elongation in a BR-deficient
mutant, an increase in the lamina bending angle, and the in-
hibition of root elongation (Figure 7). In each of these experi-
ments, the wild type was more sensitive to CS than to DS,
indicating that CS has a higher specific BR activity than DS.
DS and CS had approximately equal activity in the root inhibi-
tion assays in both the wild type and the brd2 mutant, but
brd2 was more sensitive to DS than to CS in lamina bending
assays. These results suggest a difference in tissue-specific BR
sensing.
It is noteworthy that in d61-2, which contains a lesion in rice
Bri1 kinase, BR-responsive events are not enhanced by treat-
ment with either DS or CS. This observation demonstrates that
Bri1 kinase is essential for perception of the signals triggered by
DS andCS; consequently, the signaling pathway triggered byDS
should be the same as that triggered by CS after perception by
the Bri1 kinase. At present, the reason for the higher sensitivity of
the brd2mutant to DS than to CS in the lamina bending assay is
unclear. Because lamina joint bending is a unique and hyper-
sensitive phenomenon in BR-triggering events, higher sensitivity
to DS does not directly suggest that the brd2mutant always has
higher sensitivity to DS in other tissues or organs. For example,
the root inhibition assay showed that there is no difference in the
sensitivity between DS and CS in brd2 (Figure 7C). This also
suggests the possibility that lamina joint bending of rice may be
regulated by a unique mechanism triggered by BR. In fact, its
bending is regulated not only by BR but also by auxin in
a synergistic manner (Takeno and Pharis, 1982; Cao and Chen,
1995).
METHODS
Plant Materials and Growth Conditions
The brd2mutant was obtained from rice (Oryza sativa) plants regenerated
froma suspension cell culture derived froma japonica strain,Nipponbare.
The plants were grown to maturity in the research field, and transgenic
plants were grown in a greenhouse under 16 h of illumination at 288C. For
germination, seeds were surface sterilized as described previously (Hong
et al., 2003) and plated on MS medium containing 0.8% agar. The plates
were then incubated at 308C under continuous light.
Isolation, Sequencing, and Mapping of the brd2 Gene
The Dim/dwf1 gene was identified in a BLAST search of all available rice
genomic databases. The corresponding cDNA sequence was entered as
CA757254 and AU030326, which contain the 59- and 39-flanking regions,
respectively. To identify the site of the mutation in the brd2 gene, we
amplified Dim/dwf1 by PCR and sequenced the amplified DNA fragment
with appropriate primers and without cloning. The full-length cDNA clone
was produced by RT-PCR using 1 mg of total RNA and the Omniscript RT
kit (Qiagen, Hilden, Germany). The isolated cDNA was sequenced to
confirm that no nucleotide substitutions occurred during the PCR. A clone
with the correct sequence was used to prepare probes and the sense and
antisense constructs. To map the brd2 mutant, F2 populations derived
from a cross between a plant heterozygous for brd2 and an indica strain,
kasalath, were used. Thirty plants homozygous for brd2 were identified
using molecular markers.
RNA Isolation and RNA Gel Blot Analysis
Total RNA was isolated using the RNeasy plant mini kit (Qiagen). After
incubation at 658C for 5 min, the total RNA was subjected to electropho-
resis on a 1% denaturing gel and then transferred to a Hybond Nþ
2252 The Plant Cell
membrane for RNA gel blot analysis. The probe used was a 39-terminal
cDNA fragment unless specified otherwise in the figure legends, and the
subsequent hybridization and washing were performed using the con-
ditions described by Ueguchi-Tanaka et al. (2000).
Complementation and Antisense Analyses
To isolate a genomic Dim/dwf1 clone, a BAC library was screened using
PCR. The XBH43-2B02 clone was identified as containing the entire Dim/
dwf1 gene. An 8.8-kb EcoRI fragment encompassing the full-length
Dim/dwf1 sequence and the promoter domain were fused in the SmaI
site of the hygromycin-resistant binary vector pBI-Hm12, which was
kindly provided by Hiroyuki Hirano (Tokyo University, Tokyo, Japan). The
construct was introduced into brd2 cells by Agrobacterium tumefaciens–
mediated transformation as described by Hiei et al. (1994). Control plants
were transformed with the empty vector.
To produce antisense and overexpression constructs, the full-length
cDNA was fused downstream of the rice Actin promoter in the pAct-Nos/
Hm2 vector. The orientation of the cDNA clone was determined by
restriction enzyme digestion.
Quantification of Sterols and BRs
Shoots of wild-type and mutant plants were harvested after growth in
a greenhouse for 2 months and lyophilized immediately at �808C.
Extraction and purification for BRs and sterols were performed according
to the method described by Fujioka et al. (2002) and He et al. (2003).
For BR analysis, plants (20 g FW equivalent) were extracted. [2H6]
Brassinolide, [2H6]castasterone, [2H6]typhasterol, [2H6]teasterone,
[2H6]cathasterone, [2H6]6-deoxocastasterone, [2H6]6-deoxotyphasterol,
[2H6]3-dehydro-6-deoxoteasterone, and [2H6]6-deoxoteasterone (each
1 ng/g FW) were added to the extract as internal standards. For the
analysis of 6-deoxocathasterone and sterols, plants (0.5 g FW equivalent)
were used. [2H6]episterol (100 ng), [2H7]24-methylenecholesterol (2.5mg),
[2H7]24-methylenecholest-4-en-3-one (500 ng), [2H7]24-methylene-
5a-cholestan-3-one (500 ng), [2H7]24-methylenecholestanol (500 ng),
[2H6]campesterol (10 mg), [2H6](24R)-24-methylcholest-4-en-3-one (500
ng), [2H6](24R)-24-methyl-5a-cholestan-3-one (50 ng), [2H6]campestanol
(250 ng), [2H6]6-oxocampestanol (25 ng), [2H3]cholesterol (2.5 mg), and
[2H6]6-deoxocathasterone (2.5 ng) were added to the extract as internal
standards. Purified fractions were derivatized and analyzed by gas
chromatography–mass spectrometry (GC-MS). BRs and sterols were
identified by full-scan GC-MS. The endogenous levels of episterol,
24-MC, 24-methylenecholest-4-en-3-one, 24-methylene-5a-cholestan-
3-one, 24-methylenecholestanol, CR, (24R)-24-methylcholest-4-en-3-
one, (24R)-24-methyl-5a-cholestan-3-one, campestanol, cholesterol,
and 6-oxocampestanol were calculated from the peak area ratios of
molecular ions of the internal standard and the endogenous sterol. The
endogenous level of 6-deoxocathasterone was calculated from the peak
area mass-to-charge (m/z) ratios of 193 for the internal standard andm/z
187 for the endogenous one. The endogenous levels of C29 sterols were
roughly estimated from the peak area ratios of molecular ions of internal
standards of the corresponding C28 sterols and the endogenous ones.
For instance, the level of (24R)-24-ethylcholest-4-en-3-one was calcu-
lated from the peak area ratios ofmolecular ions ofm/z 404 for [2H6](24R)-
24-methylcholest-4-en-3-one (C28 sterol, internal standard) and m/z 412
for (24R)-24-ethylcholest-4-en-3-one.
For purification and semiquantitative analysis of DS, we purified DS
according to themethod described byHe et al. (2003). Using thismethod,
the chromatographic behavior of DS was the same as BL. Purified HPLC
fraction (BL fraction: retention time, 8 to 10min) was subjected to GC-MS
analysis after methaneboronation. Based on the full mass spectrum and
retention time in GC, DS was definitely identified from the BL fraction of
brd2 mutant. Characteristic ions and retention time of DS methane-
boronate were as follows: m/z 510 (Mþ, 11), 327 (20), 153 (64), 124 (76),
82 (100); GC retention time of DS was 10.95 min (CS, 11.00 min, and BL,
11.70 min, under the same GC conditions).
The raw level was calculated from peak area at m/z 510 using
a calibration curve of authentic DS. In the first experiment, only the raw
level was shown (0.09 ng/g FW). In the second experiment, the raw level
was 0.11 ng/g FW. Because DS was detected in the BL fraction, its
endogenous level was corrected using the recovery rate of [2H6]brassi-
nolide (55%). The endogenous level was estimated to be 0.20 ng/g FW.
Lamina Joint Inclination Assay
DS and CS were dissolved in ethanol at final concentrations of 10 ng,
100 ng, and 1000 ng/mL. The seeds were germinated, and the seedlings
used in this assay were selected as described by Fujioka et al. (1998).
Six plants were used for each treatment.
Sequence data from this article may be found in the EMBL/GenBank
data libraries under the following accession numbers: rice Dim/dwf1
(AAM01136), Arabidopsis DIM/DWF1 (Q39085), and pea LKB (AAK15493).
ACKNOWLEDGMENTS
We thank Masayo Sekimoto and Makoto Kobayashi (both of RIKEN) for
their technical assistance. Youichi Morinaka, Ikuko Aichi, and Hiroko
Ohmiya (all of Nagoya University) helped with some preliminary prep-
aration. This work was supported in part by a Grant-in-Aid from the
Program for the Promotion of Basic Research Activities for Innovative
Biosciences (M.M., M.U.-T., and H.K.) and a Grant-in-Aid from the
Center of Excellence (M.M. and M.A.).
Received January 18, 2005; revised June 8, 2005; accepted June 8, 2005;
published July 1, 2005.
REFERENCES
Abe, H., Nakamura, K., Morishita, T., Uchiyama, M., Takatsuto, S.,
and Ikekawa, N. (1984). Endogenous brassinosteroids of the
rice plant: Castasterone and dolichosterone. Agric. Biol. Chem. 48,
1103–1104.
Bajguz, A., and Tretyn, A. (2003). The chemical characteristic
and distribution of brassinosteroids in plants. Phytochemistry 62,
1027–1046.
Bishop, G.J. (2001). Plants steroid hormone, brassinosteroids: Current
highlights of molecular aspects on their synthesis/metabolism, trans-
port, perception and response. Plant Cell Physiol. 42, 114–120.
Bishop, G.J., and Koncz, C. (2002). Brassinosteroids and plant steroid
hormone signaling. Plant Cell 14, (suppl.), S97–S110.
Cao, H., and Chen, S. (1995). Brassinosteroid-induced rice lamina joint
inclination and its relation to indole-3-acetic acid and ethylene. Plant
Growth Regul. 16, 189–196.
Carland, F.M., Berg, B.L., FitzGerald, J.N., Jinamornphongs, S.,
Nelson, T., and Keith, B. (1999). Genetic regulation of vascular tissue
patterning in Arabidopsis. Plant Cell 14, 2045–2058.
Carland, F.M., Fujioka, S., Takatsuto, S., Yoshida, S., and Nelson, T.
(2002). The identification of CVP1 reveals a role for sterols in vascular
patterning. Plant Cell 14, 2045–2058.
Catterou, M., Dubois, F., Schaller, H., Aubanelle, L., Vilcot, B.,
Sangwan-Norreel, B.S., and Sangwan, R.S. (2001). Brassinosteroids,
microtubules and cell elongation in Arabidopsis thaliana. I. Molecular,
An Uncommon BR Biosynthetic Pathway 2253
cellular and physiological characterization of the Arabidopsis bul1
mutant, defective in the D7-sterol-C5-desaturation step leading to
brassinosteroid biosynthesis. Planta 212, 659–672.
Choe, S., Dilkes, B.P., Gregory, B.D., Ross, A.S., Yuan, H., Noguchi,
T., Fujioka, S., Takatsuto, S., Tanaka, A., Yoshida, S., Tax, F.E.,
and Feldmann, K.A. (1999a). The Arabidopsis dwarf1 mutant is
defective in the conversion of 24-methylenecholesterol to campester-
ol in brassinosteroid biosynthesis. Plant Physiol. 119, 897–907.
Choe, S., Noguchi, T., Fujioka, S., Takatsuto, S., Tissier, C.P.,
Gregory, B.D., Ross, A.S., Tanaka, A., Yoshida, S., Tax, F.E., and
Feldmann, K.A. (1999b). The Arabidopsis dwf7/ste1 mutant is de-
fective in the D7 sterol C-5 desaturation step leading to brassino-
steroid biosynthesis. Plant Cell 11, 207–221.
Choe, S., Tanaka, A., Noguchi, T., Fujioka, S., Takatsuto, S., Ross,
A.S., Tax, F.E., Yoshida, S., and Feldmann, K.A. (2000). Lesions in
the sterol D7 reductase gene of Arabidopsis cause dwarfism due to
a block in brassinosteroid biosynthesis. Plant J. 21, 431–443.
Clouse, S.D., and Sasse, J.M. (1998). Brassinosteroids: Essential
regulators of plant growth and development. Annu. Rev. Plant Physiol.
Plant Mol. Biol. 49, 427–452.
Diener, A.C., Li, H.X., Zhou, W.X., Whoriskey, W.J., Nes, W.D., and
Fink, G.R. (2000). STEROL METHYLTRANSFERASE 1 controls the
level of cholesterol in plants. Plant Cell 12, 853–870.
Fujioka, S., Noguchi, T., Takatsuto, S., and Yoshida, S. (1998).
Activity of brassinosteroids in the dwarf rice lamina inclination bio-
assay. Phytochemistry 49, 1841–1848.
Fujioka, S., and Sakurai, A. (1997). Brassinosteroids. Nat. Prod. Rep.
14, 1–10.
Fujioka, S., Takatsuto, S., and Yoshida, S. (2002). An early C-22
oxidation branch in the brassinosteroid biosynthetic pathway. Plant
Physiol. 130, 930–939.
Fujioka, S., and Yokota, T. (2003). Biosynthesis and metabolism of
brassinosteroids. Annu. Rev. Plant Biol. 54, 137–164.
Grove, M.D., Spencer, G.F., Rohwedder, W.K., Mandava, N.B.,
Worley, J.F., Warthen, J.D., Steffens, G.L., Flippen-Anderson,
J.L., and Cook, J.C. (1979). Brassinolide, a plant growth-promoting
steroid isolated from Brassica napus pollen. Nature 281, 216–217.
He, J.X., Fujioka, S., Li, T.C., Kang, S.G., Seto, H., Takatsuto, S.,
Yoshida, S., and Jang, J.C. (2003). Sterols regulate development and
gene expression in Arabidopsis. Plant Physiol. 131, 1258–1269.
Hiei, Y., Ohta, S., Komari, T., and Kumashiro, T. (1994). Efficient
transformation of rice (Oryza sativa L.) mediated by Agrobacterium
and sequence analysis of the boundaries of the T-DNA. Plant J. 6,
271–282.
Hong, Z., et al. (2002). Loss-of-function of a rice brassinosteroid
biosynthetic enzyme, C-6 oxidase, prevents the organized arrange-
ment and polar elongation of cells in the leaves and stem. Plant J. 32,
495–508.
Hong, Z., Ueguchi-Tanaka, M., Umemura, K., Uozu, S., Fujioka, S.,
Takatsuto, S., Yoshida, S., Ashikari, M., Kitano, H., and Matsuoka,
M. (2003). A rice brassinosteroid-deficient mutant, ebisu dwarf (d2), is
caused by a loss of function of a new member of cytochrome P450.
Plant Cell 15, 2900–2910.
Jang, J.C., Fujioka, S., Tasaka, M., Seto, H., Takatsuto, S., Ishii, A.,
Aida, M., Yoshida, S., and Sheen, J. (2000). A critical role of sterols
in embryonic patterning and meristem programming revealed by the
fackel mutants of Arabidopsis thaliana. Genes Dev. 14, 1485–1497.
Klahre, U., Noguchi, T., Fujioka, S., Takatsuto, S., Yokota, T.,
Nomura, T., Yoshida, S., and Chua, N.H. (1998). The Arabidopsis
DIMINUTO/DWARF1 gene encodes a protein involved in steroid
synthesis. Plant Cell 10, 1677–1690.
McElroy, D., Zhang, W., Cao, J., and Wu, R. (1990). Isolation of an
efficient actin promoter for use in rice transformation. Plant Cell 2,
163–171.
Nomura, T., Kitasaka, Y., Takatsuto, S., Reid, J.B., Fukami, M., and
Yokota, T. (1999). Brassinosteroid/sterol synthesis and plant
growth as affected by Ika and Ikb mutations of pea. Plant Physiol.
119, 1517–1526.
Schrick, K., Mayer, U., Horrichs, A., Kuhnt, C., Bellini, D., Dangl, J.,
Schmidt, J., and Jurgens, G. (2000). FACKEL is a sterol C-14
reductase required for organized cell division and expansion in
Arabidopsis embryogenesis. Genes Dev. 14, 1471–1484.
Schrick, K., Mayer, U., Martin, G., Bellini, C., Kuhnt, C., Schmidt, J.,
and Jurgens, G. (2002). Interactions between sterol biosynthesis
genes in embryonic development of Arabidopsis. Plant J. 31,
61–73.
Schultz, L., Kerckhoffs, L.H.J., Klahre, U., Yokota, T., and Reid, J.B.
(2001). Molecular characterization of the brassinosteroid-deficient lkb
mutant in pea. Plant Mol. Biol. 47, 491–498.
Serrano-Cartagena, J., Robles, P., Ponce, M.R., and Micol, J.L.
(1999). Genetic analysis of leaf form mutants from the Arabidopsis
Information Service collection. Mol. Gen. Genet. 261, 725–739.
Souter, M., Topping, J., Pullen, M., Friml, J., Palme, K., Hackett, R.,
Grierson, D., and Lindsey, K. (2002). hydra mutants of Arabidopsis
are defective in sterol profiles and auxin and ethylene signaling. Plant
Cell 14, 1017–1031.
Takahashi, T., Gasch, A., Nishizawa, N., and Chua, N.H. (1995). The
DIMINUTO gene of Arabidopsis is involved in regulating cell elonga-
tion. Genes Dev. 9, 97–107.
Takeno, K., and Pharis, R.P. (1982). Brassinosteroid-induced bending
of the leaf lamina of dwarf rice seedlings: An auxin mediated
phenomenon. Plant Cell Physiol. 23, 1275–1281.
Tanabe, S., Ashikari, M., Fujioka, S., Takatsuto, S., Yoshida, S.,
Yano, M., Yoshimura, A., Kitano, H., Matsuoka, M., Fujisawa, Y.,
Kato, H., and Iwasaki, Y. (2005). A novel cytochrome P450 is
implicated in brassinosteroid biosynthesis via the characterization of
a rice dwarf mutant, dwarf11, with reduced seed length. Plant Cell 17,
776–790.
Tao, Y., Zheng, J., Xu, Z., Zhang, X., Zhang, K., and Wang, G. (2004).
Functional analysis of ZmDWF1, a maize homolog of the Arabidop-
sis brassinosteroid biosynthetic DWF1/DIM gene. Plant Sci. 167,
743–751.
Ueguchi-Tanaka, M., Fujisawa, Y., Kobayashi, M., Ashikari, M.,
Iwasaki, Y., Kitano, H., and Matsuoka, M. (2000). Rice dwarf mutant
d1, which is defective in the a-subunit of the heterotrimeric G protein,
affects gibberellin signal transduction. Proc. Natl. Acad. Sci. USA 97,
11638–11643.
Yamamuro, C., Ihara, Y., Wu, X., Noguchi, T., Fujioka, S., Takatsuto,
S., Ashikari, M., Kitano, H., and Matsuoka, M. (2000). Loss of
function of a rice brassinosteroid insensitive1 homolog prevents
internode elongation and bending of the lamina joint. Plant Cell 12,
1591–1605.
Yokota, T. (1997). The structure, biosynthesis and function of brassino-
steroids. Trends Plant Sci. 2, 137–143.
2254 The Plant Cell
DOI 10.1105/tpc.105.030973; originally published online July 1, 2005; 2005;17;2243-2254Plant Cell
Hasegawa, Motoyuki Ashikari, Hidemi Kitano and Makoto MatsuokaZhi Hong, Miyako Ueguchi-Tanaka, Shozo Fujioka, Suguru Takatsuto, Shigeo Yoshida, Yasuko
Brassinosteroid, DolichosteroneDIMINUTO/DWARF1, Is Rescued by the Endogenously Accumulated Alternative Bioactive
Mutant, Defective in the Rice Homolog of Arabidopsisbrassinosteroid-deficient dwarf2The Rice
This information is current as of May 22, 2021
References /content/17/8/2243.full.html#ref-list-1
This article cites 38 articles, 18 of which can be accessed free at:
Permissions https://www.copyright.com/ccc/openurl.do?sid=pd_hw1532298X&issn=1532298X&WT.mc_id=pd_hw1532298X
eTOCs http://www.plantcell.org/cgi/alerts/ctmain
Sign up for eTOCs at:
CiteTrack Alerts http://www.plantcell.org/cgi/alerts/ctmain
Sign up for CiteTrack Alerts at:
Subscription Information http://www.aspb.org/publications/subscriptions.cfm
is available at:Plant Physiology and The Plant CellSubscription Information for
ADVANCING THE SCIENCE OF PLANT BIOLOGY © American Society of Plant Biologists
